MEDICINALLY ACTIVE PLANT CHEMICALSPlants do not have an immune system like ours to protect them from attack. Instead they use chemicals to fight bacteria, fungi and insects. Because these chemicals are biologically active, some also have medicinal properties.Antimicrobials prevent the bulb rotting in wet soilGinsenosides(triterpene saponins)Protection against fungal diseasesThe tannins coagulate protein, so are an effective insect deterrentThe coagulating properties of bark tannins can be used for diarrhoeaEchinaceaEchinacea purpurea, pallida, augustifloraComplex mix of alkylamides, caffeic acid derivatives, palyalkynes and polysaccharidesAntifungal compoundsare a defence against fungal diseaseStimulates the immune system. Used for upper respiratory tract infectionsSt John’s wortHypericum perforatumHypericin and pseudohypericin (naphthodianthrones)Defence against insects that try to eat the plantBlocks neurotransmitter re-uptake. Used for depressionDeter or prevent insect or slug attackProvide its antispasmodic action. Used for indigestion
Since the 18th century scientists have been isolating the active constituents in plants. Research has given rise to some of the world’s most powerful drugs. Even today, modern medicine relies heavily on plant-derived drugs.
Not only have some of the more long-standing drugs such as digoxin, opiates and aspirin originated from plants, but many of the newer high-tech drugs such as the cancer drug vincristine and other cytotoxics (chemicals that kill cells) are also chemicals derived from plants.
Herbal medicines, however, are different from plant- derived drugs in that they consist of many chemical components. The mixture works in concert, making active constituents more easily available to the body, or buffering otherwise harmful ingredients. This means that the total therapeutic effect of the whole plant is considerably more than the sum of its chemical parts, since the active constituents’ effects will be modified by other substances. What’s more, the complex arrays of chemicals found in even the simplest plant medicines can trigger a cascade of biochemical processes in the living body. The way herbal medicines work is unlike the linear cause and effect of a single chemical (drug) acting on a single receptor system – a mechanism that pharmacologists are familiar with.
Understanding how plant medicines work calls for a leap into notions of “complexity” and “chaos” which are more familiar to physicists, than to biochemists or pharmacologists.
The consequences of using the whole plant rather than an isolated component are easily illustrated by clinical studies of garlic (Allium sativum). Recent research has shown that because garlic can lower blood pressure and cholesterol, it may be useful to people with coronary artery disease. Yet despite their best efforts, researchers have so far failed to identify which of garlic’s many chemical constituents are responsible for these medicinal virtues. Though formerly attributed to allicin, a compound found in garlic oil, it has recently become clear that the cholesterol- lowering effect of garlic results from a concerted action of several chemicals, not all of which are in the oil itself.
Research into St John’s wort (Hypericum perforatum) illustrates the same point. Trials have demonstrated that this ancient remedy is very effective in a wide range of depressive disorders, including seasonal affective disorder. It is as effective as modern antidepressant drugs in treating mild to moderate depression, but provokes virtually none of their side-effects. Researchers, however, cannot as yet assign the plant’s antidepressant effects to specific chemical components. Another group of chemicals with huge medicinal potential that is not yet well understood are flavonoids. These are chemical compounds that give many flowers, fruits and vegetables their colour. They display an amazingly broad range of medicinal activity: improving capillary fragility and circulation, protecting the liver and preventing heart attacks and strokes. Some are antioxidant or anti-inflammatory and antiviral, while others have demonstrable anticancer properties.
The rapidly expanding body of research into plant pharmacology is challenging the very basis of drug-based medicine. The realisation that many apparently minor chemical constituents, until recently overlooked, have significant medicinal properties has come as a revelation.
Herbal practice relies on the gentle and supportive nature of the remedies it uses. In contrast to conventional medicine, herbal practitioners focus on the person rather than the disease label. The herbal practitioner will explore the background of the illness taking a comprehensive case history, in which family and personal life are carefully evaluated. Questions cover lifestyle, exercise and diet, as well as how the patient feels about his or her circumstances (job, relationships, aspirations and anxieties). Then the practitioner is likely to perform a physical examination and may order clinical tests. All this information is used to assess the vitality of the patient, and establish which systems are sluggish and which are overworked. The practitioner will prescribe a mixture of herbs accordingly.
The herbal prescription is not a simple matter of using herbs in the place of drugs to treat a particular condition. Drugs are standardised, while herbal treatment rarely is. Each prescription is unique to the patient, matching the needs of that person, supporting ailing systems and/or reducing over-activity when it is apparent.
In practice, herbs are not usually used as “simples” (i.e. given singly), but are combined for extra effect to suit the individual. St John’s wort, for example, though marketed as a remedy to treat mild to moderate depression, is commonly combined with other herbs. When St John’s wort is combined with lemon balm (Melissa officinalis), it is used to treat anxiety and depression; with wild oat (Avena fatua) and/or ginseng (Panax ginseng), it is given for exhaustion; with valerian (Valeriana officinalis), it is a treatment for bipolar mood disorder.
Herbs often confer a wide spectrum of benefits. For example, lemon balm can be used for anxiety and insomnia, but it is also traditionally used for calming a nervous stomach and bowel. Recently it has been found to have a significant antiviral effect and may also help in the treatment of hyperthyroidism. Herbal remedies can support and stimulate the body’s healing response. The herbalist and the patient are partners in this aim, working together towards the common goal of restoring health.
It is clear that “natural” does not always equal “safe”, and that herbal medicines, like conventional medicines, can cause adverse effects. Such adverse events may also be due to contaminants present in herbs, such as heavy metals or aflatoxins, or even because of misidentification of a herb. There is a possibility of herb-drug interactions too (see below), Therefore herbal practitioners must be very well trained and know exactly what other medicines their patients are taking.
Safety concerns should be set in context. The European Herbal Practitioners’Association estimates that in 2003 there were over a million herbal consultations in the UK. According to a BBC poll (August 1999), herbal medicines are the most popular form of self-care.
It would appear that the incidence of herbal adverse effects is rather low. A five-year study into the occurrence of adverse events involving traditional herbal medicines and food supplements was undertaken by the UK National Poisons Unit. Of the 1,297 enquiries received, a medicine was implicated as a probable cause of the adverse events in only 38 cases. The Ministry of Agriculture, Fisheries and Food commented: “The findings overall are reassuring as they do not indicate any significant health problems associated with most types of traditional remedies and dietary supplements.” However, there have been a number of important concerns regarding the safety of herbal medicines in the past two decades. Using toxic Aristolochia species instead of safer herbs in some traditional Chinese medicines resulted in cases of serious kidney poisoning and cancer in Europe, China, Japan and the US.
Volatile oils such as menthol and thymol have a pungent aromatic aroma and a range of actions because they penetrate easily through the body’s tissues. Their molecules can even affect the brain directly through the nose. Herbalists have long known that the aroma of crushed mint (Mentha) or rosemary (Rosmarinus officinalis) can increase alertness and improve concentration. Internally, these oils are carminative, relaxing an over-contracted intestinal tract. They also stimulate the heart and lungs, improving circulation and deepening breathing. These oils are excreted through the lungs, kidneys and skin, so they act as expectorants and mild diuretics, causing therapeutic sweating. The traditional germicidal properties of many volatile oils, such as from thyme (Thymus), tea tree (Melaleuca alternifolia) and garlic (Allium sativum), are effective to a surprising degree. Garlic has recently been shown to combat the common cold and the hospital superbug MRSA.
Professor Ernst, Chair of Complementary Medicine at the University of Exeter, has recently downplayed the threat of adverse effects from herbal medicines. In an editorial in the British Medical Journal he comments that “Even though herbal medicines are not devoid of risk, they could still be safer than synthetic drugs. Between 1968 and 1997, the World Health Organization’s monitoring centre collected 8985 reports of adverse events associated with herbal medicines from 55 countries. Although this number may seem impressively high, it amounts to only a tiny fraction of adverse events associated with conventional drugs held in the same database. However, the relative paucity could also be due to a relatively higher level of underreporting
At present, the relative safety of herbal medicines is undefinable, but many of the existing data indicate that adverse events, particularly serious ones, occur less often than with prescription drugs.”
Only a tiny fraction of herbal medicines have been fully researched. In some cases, this has led to doctors doubting their efficacy. However, in the same editorial, Professor Ernst dispels the myth that herbal remedies are ineffective and lack credibility because they have not been researched. He writes, “The efficacy of herbal medicines has been tested in hundreds of clinical trials, and it is wrong to say that they are all of inferior methodological quality. But this volume of data is still small considering the multitude of herbal medicines – worldwide several thousand different plants are being used for medicinal purposes.”
Relatively few rigorous clinical trials have been conducted on herbal therapies mainly because, compared with the pharmaceutical sector, the herbal industry can rarely afford the considerable expense of a clinical trial.
Not being able to patent plant medicines and recoup the costs as drug companies are able to do, puts the herbal industry at a very real disadvantage. However, most of those clinical trials that have been conducted have shown that herbal medicines do work. In a recent overview of 23 systematic reviews (which are comparative and critical analyses of many research studies) of rigorous trials of herbal medicines, 11 came to a positive conclusion, nine yielded promising but not convincing results, and only three were actually negative.
In most developed countries, herbal medicines are subject to increasing regulation. Most major professional herbal associations are now reporting any side-effects so information may be shared among professionals. Proposed new European Union and UK medicines legislation will ensure medicinal plants are identified correctly. The European Directive on Traditional Herbal Medicinal Products, which became law in 2004, requires that over- the-counter herbal remedies should demonstrate at least 30 years of safe use to qualify for registration. Herbal remedies are now being officially listed for safety and efficacy by the European Medicines Evaluation Agency (EMEA). In 2003, the Herbal Medicine Regulatory Working Group set up by the British government published a report calling for the immediate statutory regulation of all UK herbal pract¬itioners. This means that British herbalists will be regulated and acknowledged by the state and other fellow health professionals, thereby ensuring that herbal medicines, which have been tried and tested over hundreds of years, will continue to play a part in everyday healthcare.
Herbal remedies, like all medicines, must be treated with respect. There are certain conditions and combinations of treatments in which herbs may cause problems.
General cautions
During the first three months of pregnancy, avoid all medicines, herbal or otherwise, unless absolutely essential.
• Certain herbs should be avoided throughout pregnancy, so consult a qualified medical herbalist.
• Women who are breast-feeding should consult a medical herbalist before using herbal medicines.
• Do not give babies under 6 months any internal herbal (or other) medicine without professional advice.
• The elderly, because of their slower metabolism, may require less than the full adult dose.
• Do not stop taking prescribed conventional medication without first consulting your doctor.
• Some herbs interact with drugs. If you are taking a prescribed medicine, consult a medical herbalist.
Herb-drug interactions
Herbs can change the way that your body absorbs and breaks down (metabolises) drugs. They can also affect other aspects of your metabolism, e.g. heart rate and blood pressure, which can mask or exacerbate symptoms. If herbs and drugs have similar actions, the combined effect can be too strong. This list of cautions is a guide to some of the potential drug interactions and situations when herbs should be used with care. Consult a medical herbalist about herb-drug interactions and contraindications.
Coltsfoot (Tussilago farfara) in excessive doses may interfere with blood pressure treatment. Also avoid long-term use.
Garlic (Allium sativum) in medicinal doses can cause a dangerous decrease in blood-sugar levels if taken with diabetes medication. Do not take it with the blood- thinning drug warfarin or other anti-clotting medication. (Culinary amounts of garlic are safe.)
Ginkgo (Ginkgo biloba) should not be taken with warfarin or other anti-clotting medication.
Ginseng, Siberian (Eleutherococcus senticosus) can increase blood pressure, so it should be avoided by anyone with this condition.
Goldenseal (Hydrasatis canadensis) can raise blood pressure. Consult a qualified herbalist if taking beta- blocker or other antihypertensive medications, or medication to control diabetes or kidney disease. Hawthorn (Crataegus spp.) may interact with other medicines, especially those prescribed for heart conditions. Hops (Humulus lupulus) have a mild sedative effect and act as a depressive. Do not take if you have depression, breast cancer, or other oestrogen-responsive cancers. Do not take with alcohol.
Lily of the valley (Convallaria majalis) contains cardiac glycosides and may interact with other heart drugs. It should only be taken when prescribed by a qualified medical herbalist.
Liquorice (Glycyrrhiza glabra) should not be taken by anyone who is anaemic, or has high blood pressure. Schisandra (Schisandra chinensis) should possibly be avoided by those with epilepsy or hypertension.
St John’s wort (Hypericum perforatum) increases the rate at which the liver breaks down drugs, so that a drug taken alongside it may not be effective. Drugs that may be affected include indinavir and other drugs used for HIV infection, as well as warfarin, cyclosporin, digoxin, theophylline and possibly oral contraceptives. St John’s wort may also cause sensitivity to sunlight, though this is most unusual within normal dosage range.
WHEN TO CONSULT A PRACTITIONER
The UK National Institute of Medical Herbalists and the National Herbalists’ Association of Australia keep registers of trained medical herbalists. Your doctor may also be able to make a recommendation. You should consult a medical herbalist before taking herbal medicines if you are pregnant or have a serious condition such as diabetes, heart disease or high blood pressure. Do not stop taking prescribed medication without first consulting your doctor. Some herbs and drugs interact – see above before taking a herbal medicine.
